If you can install through Slack, why are you trying to install it through cabal ? Have you put parsec as a dependency of your project ? (In the cabal file or package.yaml file, depending on which version of Slack you use) In which case, you should be able to use parsec as a dependency (or test it in an interpreter launched using stack ghci).
– RavelineMay 17 at 10:03

Did you try updating Xcode to the latest version (this will also update clang)?
– David YoungMay 17 at 18:49

Thank you for your kind replies. David Young> I must update the computer system in order to update Xcode. I will try it after exam time. :)
– Etienne BernardMay 18 at 18:25

1 Answer
1

But! I’ve seen that suggestions since 2013, and in that case, I can’t update Xcode, because I have old Macbook and OS X 10.11 on it, i have tried:
brew install gcc
Next step I wondering how to setup Gnu C Compler over Xcode and found right now how.
Open in terminal with your fav. editor: